I'm guessing the large jump down to 65 jets were to see that the O2 sensor was responding as it should. A small jet change might have gotten 'lost', where a big change should be easily seen. As long as he didn't run it into detonation (and I'm sure he knows better), the big change didn't hurt anything. Now, if he were to try to do a full pull that way, I'd stop him- unless it wasn't running lean jetted like that. And I have to assume he knows what he's doing. But all that said, mistakes are made- even by the best. It's your engine and your "dime", so if there's any question in your mind, you HAVE to speak up.